Search results for "Pressure dependence"
showing 10 items of 22 documents
Streulichtuntersuchungen an exotherm-pseudoidealen Lösungen in Abhängigkeit von Druck und Temperatur
1971
Fraktionierte Proben von Polyisobutylen (PIB) (Mw = 73 500 und 690 000) wurden in n-Pentan (70–85°C) und in i-Octan (15–45°C) bei Drucken bis zu 1000 atm untersucht. An beiden Systemen beobachtet man eine ausgepragte Zunahme des zweiten osmotischen Virialkoeffizienten A2 mit steigendem Druck und eine wesentlich schwachere Abnahme mit steigender Temperatur. Eine genauere Analyse ergibt folgendes Bild: Der bei verschiedenen konstanten Drucken aus der Temperaturabhangigkeit von A2 ermittelte A2,H-Wert nimmt mit steigender Temperatur zu und mit steigendem Druck ab; dieser Befund steht im Einklang mit den Ergebnissen der fruheren Untersuchungen [1 – 3]. Im vorliegenden Fall bedeutet er, das die …
Pressure Dependence of Positron Annihilation in Si
1994
The pressure dependence of the electron-positron and the electron-electron momentum densities in silicon are studied. The observations that the electron-positron momentum density increases more rapidly with pressure than the electron-electron momentum density alone is explained in terms of increased positron penetration into the ion cores. The computational technique used here is based on the independent-particle model (IPM) coupled with the use of the electron pseudo-wave functions.
Pressure dependence of optical phonons in ZnCdSe alloys
2003
5 páginas, 2 figuras, 2 tablas.-- PACS 62.50.+p, 63.20.Dj, 78.30.Fs, 78.66.Hf.-- et al.
Pressure-Induced Hexagonal to Monoclinic Phase Transition of Partially Hydrated CePO4
2019
We present a study of the pressure dependence of the structure of partially hydrated hexagonal CePO 4 up to 21 GPa using synchrotron powder X-ray diffraction. At a pressure of 10 GPa, a second-order structural phase transition is observed, associated with a novel polymorph. The previously unknown high-pressure phase has a monoclinic structure with a similar atomic arrangement as the low-pressure phase, but with reduced symmetry, belonging to space group C2. Group-subgroup relations hold for the space symmetry groups of both structures. There is no detectable volume discontinuity at the phase transition. Here we provide structural information on the new phase and determine the axial compress…
Band-to-Band and Band-to-Acceptor Photoluminescence Studies in InSe under Pressure
1999
We report on photoluminescence (PL) measurements under pressure on p-type N-doped InSe at 10 K and on n-type Si-doped InSe at room temperature. Low-temperature PL of N-doped InSe is dominated by a band-to-acceptor peak. From the pressure dependence of the ionization energy of the N related shallow acceptor, the pressure change of the hole effective mass is estimated through the Gerlach-Pollmann model for hydrogenic levels in uniaxial crystals and discussed in the framework of a k p model. Room temperature PL in Si-doped InSe is dominated by a band-to-band peak exhibiting a pressure shift in agreement with previous works. This PL peak has been measured up to 7 GPa and a steep reversible decr…
Pressure-dependent modifications in the optical and electronic properties of Fe(IO3)3: the role of Fe 3d and I 5p lone–pair electrons
2021
We have determined by means of optical-absorption experiments that Fe(IO3)3 is an indirect band-gap material with a band-gap energy of 2.1 eV. This makes this compound the iodate with the smallest band gap. We also found that under compression the band-gap energy has an unusual non-linear pressure dependence, which is followed by an abrupt and discontinuous decrease of the band gap at 24 GPa. The observed behavior is explained by means of density-functional calculations, which show that the behavior of the band gap is governed by the combined influence of Fe 4d and I 5p lone pair electrons. In addition, the abrupt decrease of the band-gap energy at 24 GPa is a consequence of a first-order s…
Pressure and temperature dependence of the lattice dynamics ofCuAlO2investigated by Raman scattering experiments andab initiocalculations
2006
We have studied the vibrational properties of $\mathrm{Cu}\mathrm{Al}{\mathrm{O}}_{2}$ by means of Raman scattering in ambient conditions, at low temperature, and also at high pressure. Results are discussed in the framework of an ab initio calculation. Raman active modes have wave numbers ${\ensuremath{\sigma}}_{{E}_{g}}=418.1\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and ${\ensuremath{\sigma}}_{{A}_{1g}}=767.2\ifmmode\pm\else\textpm\fi{}0.3\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Polarized measurements with single crystals have confirmed their symmetry. We present and discuss the phonon-dispersion curves. Below $200\phant…
Pressure Dependence of the Bandgap Bowing in Zinc-Blende ZnTe 1− x Se x
2002
We report on the pressure dependence of the bandgap bowing in the ZnTe 1 m x Se x alloy, in the whole composition range. The bandgap bowing parameter is shown to increase almost linearly with pressure from 1.23 at ambient pressure to 1.6 at 7 GPa. Saturation effects observed in the pressure dependence for x =0.1 and x =0.2 are shown to be related to the direct-to-indirect crossover. Results are discussed and interpreted in the framework of structural relaxation models for gap bowing. A prediction of these models (the negative bowing of the o 15 m ;X 1 transition) is shown to be compatible with the fact that the direct-to-indirect crossover pressure increases with the Se content.
Pressure-induced band anticrossing in two adamantine ordered-vacancy compounds: CdGa2S4 and HgGa2S4
2021
Abstract This paper reports a joint experimental and theoretical study of the electronic band structure of two ordered-vacancy compounds with defect-chalcopyrite structure: CdGa2S4 and HgGa2S4. High-pressure optical-absorption experiments (up to around 17 GPa) combined with first-principles electronic band-structure calculations provide compelling evidence of strong nonlinear pressure dependence of the bandgap in both compounds. The nonlinear pressure dependence is well accounted for by the band anticrossing model that was previously established mostly for selenides with defect chalcopyrite structure. Therefore, our results on two sulfides with defect chalcopyrite structure under compressio…
Pressure dependence of density and structural relaxation of glass near the glass transition region
2017
International audience; A simplified and effective pressure cell together with an experimental procedure has been developed and applied to compress samples of SCHOTT N-BK7 glass under static high pressures in a piston-cylinder apparatus. Results from the density and volume recovery measurements show that, the glass samples were effectively densified in piston-cylinder apparatus with the density at room temperature increasing linearly with frozen-in pressure. To explain the experimental data, we developed a mathematical model based on a suggestion by Gupta (1988) with two internal parameters, named fictive temperature (Tf) and fictive pressure (Pf), which fits the experimental data well.